Annunciator circuit

ABSTRACT

An annunciator circuit comprising means for generating an output level signal in response to a sensed abnormal signal condition, an audible alarm, and means for actuating the audible alarm upon initial recognition of the output level signal from the generating means and only for the duration of the output level signal. Acknowledgement means electrically coupled to the alarm actuating means is also provided for deactuating the audible alarm only while the abnormal signal condition is sensed and for the duration of the output level signal.

[ July 1, 1975 3 1972 Erpeldingmm......,m.,.......340/2131 ABSTRACT An annunciator circuit comprising means for generating an output level signal in response to a sensed abtion of the output level signal from the generating means and only for the duration of the output level signal. Acknowledgement means electrically coupled m. m f

o bn .m et mm d R mm m w F r VJ 05 m .m OM W m md mm 1 e S M .m me a h u nC E g am .m u t amu m w ch 880 Primary ExaminerThomas B. Habecker Attorney, Agent, or FirmS. A. Young; W, C, Bernkopf normal signal condition, an audible alarm, and means for actuating the audible alarm upon initial recogni to the alarm actuating means is also provided for de- ANNUNCIATOR ClRCUlT Inventor: Art Lee, El Paso, Ill.

Assignee: General Electric Company, New

York, N.Y.

Filed: Dec. 3, 1973 Appl. No.: 420,870

US. IMO/213.1; 340/415; 307/252 L Int. G08b 25/00- Field of Search.................

References Cited UNITED STATES PATENTS United States Patent Lee Walsh,.,,...i....,...,... Thomason et a1. Monigal et al...... Judlowe...i..,........,.....i

PUL SE GENERATOR 1 ANNUNCIATOR CIRCUIT BACKGROUND OF THE INVENTION l. Field of The Invention This invention relates to an annunciator card including an annunciator circuit. and more particularly to an improved annunciator circuit.

2. DESCRIPTION OF THE PRIOR ART Annunciator circuits of the types described in US. Pat. No. 3.688.294 are comprised of an abnormal signal condition sensing circuit. a differentiator circuit coupled to the sensing circuit. a silicon controlled rectifier memory element and logic means for driving an au dible alarm and intermittently driving a visual alarm while current is flowing through the memory element. and for providing steady state drive for the visual alarm after the SCR memory element is deactuated while an abnormal signal condition is still being sensed. The SCR memory element is actuated by a trigger signal produced from the output of the differentiator circuit upon the initial sensing (recognition) of the abnormal signal condition. While the SCR memory element is actuated. the audible alarm remains actuated while the visual alarm flashes intermittently. These visual and audible alarm indications continue even if the abnormal signal condition has ceased or has been repaired. and until someone finally depresses an acknowledgement button which interrupts the flow of current through the SCR memory element. Thus. if there is no one near the acknowledgement switch. the audible and visual alarms continue to provide alarm indications and consume energy even if the sensed abnormal condition has been corrected Furthermore. in annunciator circuits of the type described above. the sensed abnormal signal condition is directly electrically coupled to the annunciator circuit and there is no electrical isolation between the sensed signal condition and the trigger signal for actuating the SCR element.

Still further. an annunciator system is usally comprised of an plurality of annunciator cards. wherein each card includes an annunciator circuit of the type described above for sensing a specific abnormal condition Power is generally supplied to each of these cards from an external source. Thus. if the external power source were sufficient to supply power to 30 cards. and if the system were suddenly expanded to 32 cards. an additional power source would be required at an additional cost.

OBJECTS OF THE INVENTION It is therefore an object of this invention to provide an annunciator circuit which will allow its visual and audible alarms to be deactuated ifthe sensed abnormal signal condition has been corrected. even when the acknowledgement switch has not been depressed.

It is another object of this invention to provide an annunciator card which includes an annunciator circuit thereon having its own internal power source for supplying power to an audible alarm through an SCR element.

It is another object of this invention to provide an annunciator circuit which generates an output level signal for triggering an SCR element. which output level signal is electrically isolated from a sensed abnormal signal condition.

Other objects of the invention will be pointed out in and understood from the following.

SUMMARY OF THE INVENTION According to a broad aspect of the invention there is provided an annunciator circuit comprising means for generating an output level signal in response to a sensed abnormal signal condition. an audible alarm. and means for actuating the audible alarm upon initial recognition of the output level signal from the generating means and only for the duration of the output level signal. Acknowledgement means electrically coupled to the alarm actuating means is also provided for deactuating the alarm actuating means and the audible alarm only while the abnormal signal condition is sensed and for the duration of the output level signal. The annunciator circuit is further comprised of a visual alarm means. a pulse generator. and a first logic driver means responsive to actuation of the alarm actuating means and output pulse signals from the pulse generator for intermittently driving the visual alarm means to cause the visual alarm means to flash on and off. and thereby produce an intermittent visual alarm indication. Further provided is a second logic driver means responsive to the output level signal from the generating means and to deactuation of the actuating means for continuously driving the visual alarm means to cause the visual alarm means to produce a steady state alarm indication. The generating means is comprised of a photoelectric or Hall Effect transducer for converting the sensed abnormal signal condition in the form of a DC or AC signal to the output level signal which is electrically isolated from the sensed abnormal signal condition. The generating means. the actuating means. the visual alarm means. and the first and second logic driver means are located on an annunciator card for sensing a specific abnormal signal condition. This card includes thereon a means for supplying DC power to the generating means. the actuating means and the second logic driver means. The DC. power means is electrically coupled to DC. power means of other annunciator cards for sharing power therebetween.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a schematic diagram of the annunciator circuit according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, the invention will now be described.

Each condition to be sensed by an annunciator circuit results in the generation of an abnormal signal condition in the form of either an AC or DC signal as represented by signal source 10, wherein generation of an AC or DC signal can be indicative of a sensed problem on an assembly line of a factory or can be indicative of any other monitored problem. Each sensed signal con dition is electrically connected to an annunciator circuit associated with a specific annunciator card 12.

Located on the annunciator card is a means 14 for generating an output level signal in response to the sensed abnormal signal condition, an audible alarm l6, a means 18 for actuating audible alarm I6 upon initial recognition of the output level signal from generating means 14 and only for the duration of the output level signal, a visual alarm means 20, a first logic driver means 22, a second logic driver means 24, a first out signal means 26, a means 28 responsive to a generated first out signal means of another annunciator circuit, and a DC power supply means 30. Located externally of annunciator card 12 is audible alarm 16, a clock or pulse generator 32 and an acknowledgement means 34.

Generating means 14 has an input terminal A electrically connected to signal source 10, and an output ter minal B electrically connected to input terminals C and D of alarm actuating means 18, an input terminal E of second logic driver means 24, and an external test terminal T,. Generating means 14 converts the sensed AC or DC signal, which indicates a sensed abnormal signal condition. to, in this embodiment, a positive output level signal at output terminal B. As soon as the abnormal condition ceases or is corrected. the corresponding AC or DC signal decreases to zero voltage, while the output level signal at terminal 8 also simultaneously decreases to zero voltage. Since generating means 14 is comprised of a suitable photoelectric or Hall Effect transducer, the output level signal is electrically isolated from the sensed AC or DC signal.

The photoelectric transducer is comprised of a photo-diode (not shown) which is optically coupled to a photo-transistor of a photo-transistor amplifier (not shown) and the output of the photo-transistor amplifier is electrically coupled to an inverter amplifier (not shown). Thus, when an AC or DC signal is sensed at source 10, the photo-diode conducts current, and turns on the photo-transistor of the photo-transistor amplifier. When the photo-transistor turns on, the input to the inverter amplifier is at zero voltage level, and the desired positive output level signal is produced at the output terminal of the inverter amplifier, which output level signal is electrically coupled to output terminal B of generating means 14. When source is at zero voltage, the photo-diode is not conducting and the phototransistor is in the off condition. Under these circumstances, a voltage is applied to the input of the inverter amplifier which is sufficient to cause the output of the inverter amplifier and terminal B to be at zero voltage level.

Actuating means 18 is comprised of a differentiator circuit which includes a capacitor 36 and a resistor 38. One terminal of capacitor 36 is electrically connected to input terminal C of actuating means 18, and its other terminal is electrically connected to one terminal of resistor 38. The other terminal of resistor 38 is electrically connected to the annunciator circuit ground. Ac tuating means 18 is further comprised of blocking diodes 40, 42 and 43, a silicon controlled rectifier 44, a transistor 46 and resistors 48 and 50. Blocking diode 40 has its anode electrically connected to the juncture of capacitor 36 and resistor 38, while its cathode is electrically connected to the gate electrode of silicon controlled rectifier 44. Blocking diode 42 has its anode electrically connected to an output terminal F of acknowledgement means 34, while its cathode is electrically connected to the anode of silicon controlled rectifier 44. The cathode of silicon controlled rectifier 44 is electrically connected to the collector of transistor 46. The base of transistor 46 is electrically coupled to input terminal D of actuating means 18 via biasing resistor 48. The emitter of transistor 46 is electrically connected to an input terminal G of second logic driver means 24, and input terminal H of first logic driver means 22 and an input terminal J of first out signal means 26. The emitter of transistor 46 is also connected to the anode of blocking diode 43 and one terminal of resistor 50. The other terminal of resistor 50 is electrically connected to the annunciator circuit ground. and the cathode of blocking diode 43 is electrically connected to audible alarm 16. Audible alarm 16 can be comprised of a standard buzzer or bell.

Second logic driver means 24 is comprised of an inverter amplifier 52, resistors 54, 56, 58, 60 and 62, transistors 64 and 66 and a blocking diode 68. Amplifier 52 is a standard inverter amplifier, and its input terminal is electrically connected to input terminal G of second logic driver means 24, while its output terminal is electrically connected to the base terminal of transistor 64. The base terminal transistor 64 is also electrically connected to one terminal of resistor 54, while the other terminal of resistor 54 is electrically connected to the annunciator circuit ground. The collector of transistor 64 is electrically connected to one terminal of re sistor 56, while the other terminal of resistor 56 is electrically connected to an output terminal K of DC power means 30. The emitter of transistor 64 is electrically connected to the collector of transistor 66, while the emitter of transistor 66 is electrically coupled to the am nunciator circuit ground via resistor 62. The emitter of transistor 66 is also electrically connected to the anode of diode 68, while the cathode of diode 68 is electrically connected to an input terminal L of visual alarm means 20. The base of transistor 66 is electrically connected to input terminal E of second logic driver means 24 via resistor 58, and input terminal E is also electrically coupled to the circuit ground via resistor 60.

First logic driver means 22 is comprised of resistors 70, 72, 74 and 76, a transistor 78 and a blocking diode 80. Input terminal H of first logic driver means 22 is electrically coupled to the base of transistor 78 via resistor 70. The base of transistor 78 is also electrically coupled to the circuit ground via resistor 72. The emitter of transistor 78 is electrically connected to input terminal L of visual alarm means 20, and also is electrically coupled to the circuit ground via resistor 76. The collector of transistor 78 is electrically coupled to the cathode of blocking diode 80 via resistor 74. The anode of diode 80 is electrically connected to an output terminal M of clock or pulse generator 32. Generator 32 can be any standard commercially available or specially designed pulse generator having the desired pulse repetition rate and duty cycle.

Visual alarm means 20 is comprised of lamps 82 and 84 connected in parallel, biasing resistors 86 and 88, a blocking diode 90 and a lamp driver transistor 92. One end of respective lamps 82 and 84 is electrically con nected to an external source of DC power via a high voltage terminal N. In this instance the external source ofDC power can be volts. The other end of respective lamps 82 and 84 is electrically connected to the collector of transistor 92. The emitter of transistor 92 is electrically connected to the annunciator circuit ground, while its base is electrically connected to the common juncture of resistors 86 and 88. The other end of resistor 88 is electrically connected to the annunciator circuit ground, while the other end of resistor 86 is electrically connected to the cathode of blocking diode 90. The anode of blocking diode 90 is electrically con nected to an external test point T DC power means 30 is comprised of a voltage drop ping resistor 94 and a zener diode 96. The anode of zener diode 96 is electrically connected to the annunciator circuit ground, while the cathode is electrically connected to output terminal K of DC power means 30. One end of resistor 94 is electrically connected to the cathode of Zener diode 96, while the other end of resistor 94 is electrically connected to high voltage terminal N. Zener diode 96 is selected to have a voltage breakdown of the desired value necessary to supply voltage from terminal K to generating means 14, inverter 52, and transistors 64 and 66 via resistor 56. Power from output terminal K of supply means 30 is also supplied to silicon controlled rectifier 44 and transistor 46 of actuating means 18 via a voltage dropping resistor 98, acknowledgement means 34 and blocking diode 42. A low voltage terminal P, which is electrically coupled to terminal K via resistor 98, is electrically connected to its counterpart low voltage terminals of other annunciator cards, and in this manner the low voltage power of all the annunciator cards of the annunciator system is interconnected and shared when necessary. At this point it is noted that acknowledgement means 34 is comprised of a normally closed pushbutton switch 100.

First out signal means 26 is comprised of a diode 102. The anode of diode 102 is electrically connected to input terminal J of first out signal means 26, while the cathode of diode 102 is electrically connected to a first out signal terminal 0. First out signal terminal Q is electrically connected to its counterpart terminals of other annunciator cards in the system.

Means 28, responsive to a generated first out signal means of another annunciator circuit, is comprised of a biasing resistor 104 and a transistor 106. The collector of transistor 106 is electrically connected to the anode of blocking diode 40, while the emitter of transistor 106 is electrically connected to the annunciator circuit ground. The base of transistor 106 is electrically connected to one end of resistor 104, while the other end of resistor 104 is electrically connected to first out signal terminal Q and the cathode of diode 102.

Operation of the annunciator circuit will now be explained. As previously described, upon the sensing of an abnormal condition, a signal is applied to input terminal A of generating means 14, whereupon an output level signal is generated at output B of generating means 14. In response to initial recognition of the output level signal, transistor 46 of alarm actuating means 18 is biased on, and a trigger pulse is produced by the differentiator circuit of alarm actuating means 18. Since, in this instance, the output level signal is a positive step signal, the trigger pulse is a positive signal, which passes through blocking diode 40, and turns on silicon controlled rectifier 44. When this occurs, current, which is supplied from DC power means 30, passes through resistor 98, acknowledgement switch 100, blocking diode 42, and then through silicon con trolled rectifier 44 and transistor 46. The current flowing through transistor 46 continues to flow from its emitter to the annunciator circuit ground via resistor 50, and to audible alarm 16 via blocking diode 43. Alarm 16 generates an audible signal as long as silicon controlled rectifier 44 remains actuated. Similarly cur rent continues to flow from the emitter of transistor 46 to the base of transistor 78 via resistor 70 of first logic driver means 22. Since output signal pulses from pulse generator 32 are applied to the collector of transistor 78 via blocking diode 80 and resistor 74, current pulses flow through transistor 78 and its emitter to the base of lamp driver transistor 92 of visual alann means 20. These current pulses, applied to the base of transistor 92, cause transistor 92 to be intermittently actuated, which, in turn, allows current pulses to flow through lamps 82 and 84. Lamps 82 and 84 flash on and off to provide a visual indication that an abnormal signal condition has been sensed but not yet acknowledged by the person responsible for its acknowledgement.

At this point it should be noted that current, which is flowing from the emitter of transistor 46, is also flowing through diode 102 of first out signal means 26 to first out signal terminal Q. Current continues to flow from first out signal terminal Q to its counterpart terminals on other annunciator cards to prevent actuation of the alarm actuating means of other annunciator circuits while current is flowing through silicon controlled rectifier 44. Similarly, current flowing through diode 102 also flows to the base of transistor 106 via resistor 104, thus causing transistor 106 to be turned on and effectively clamp the anode of diode 40 to the circuit ground.

Silicon controlled rectifier 44 remains actuated until acknowledgement switch is depressed by the person responsible therefor so as to cause the interruption of the flow of current through silicon controlled rectifier 44. However, if it is not convenient for someone to depress acknowledgement switch 100, and such action is not forthcoming within a resonable time, the flow of current through silicon controlled rectifier 44 can be interrrupted as follows. If, in the interim, the abnormal condition is repaired or ceases to malfunction, the sensed signal condition at terminal A or generating means 14 decreases to zero volts, thereby causing the sensed signal condition at output terminal B to decrease to zero volts, which, in turn, causes transistor 46 to turn off. As soon as transistor 46 is turned off, silicon controlled rectifier 44 is deactuated. Upon deactuation of silicon controlled rectifier 44, current ceases to flow to audible alarm 16, thereby causing its deactuation. Similarly, current ceases to flow to the base of transis tor 78 of first logic driver means 22, thereby causing transistors 78 and 92 to turn off and lamps 82 and 84 to cease flashing. Also, current is no longer flowing through diode 102 of first out signal means 26, so that the anode of blocking diode 40 is no longer clamped to the circuit ground, and the alarm actuating means of other annunciator circuits is no longer inhibited from being actuated. [f silicon controlled rectifier 44 is deactuated in response to cessation of the abnormal condition, zero voltage at output terminal B is applied at the base of transistor 66 to bias transistor 66 off. Thus, no current can flow through transistor 66 and diode 68 to the base of lamp driver transistor 92, and there is no further actuation of the visual and audible alarm.

However, if there is an output level signal prsent at output terminal 8 of generating means l4, and silicon controlled rectifier 44 has become deactuated by the opening of acknowledgement switch 100, then the annunciator circuit produces a steady state visual alarm indication as follows. Since no current is flowing through transistor 46, inverter amplifier 52 of second logic driver means 24 is turned off so as to cause a posi tive signal to be applied to the base of transistor 64 to bias transistor 64 on. Since the output level signal at output B of generating means 14 is electrically coupled to the base of transistor 66 via resistor 58, transistor 66 is also biased on. Thus, current flows through transistors 64 and 66, and through blocking diode 68 to the base of lamp driver transistor 92. The application of the steady state drive current to transistor 92 enables current to flow through lamps 82 and 84 and transistor 92, whereby lamps 82 and 84 are lit to provide a steady state alarm for indicating that a sensed abnormal signal condition has been acknowledged but not yet corrected. At this point it should be noted that when silicon controlled rectifier 44 is actuated. current flows from the emitter of transistor 46 to the input ofinverter amplifier 52. This causes the output of inverter amplifier 52 to be at a zero voltage level, which. in turn, causes transistor 64 to be biased off, so that no current can flow through transistors 64 and 66 and therefore no steady state current can flow to the base of lamp driver transistor 92.

It should also be noted that when the silicon controlled rectifier of any other annunciator card is acutated, current flows through terminal and resistor 104 to the base of transistor 106 so as to clamp the anode of blocking diode 40 to the circuit ground, which, in turn, prevents any trigger signal from penetrating therethrough to the gate of the silicon con trolled rectifier 44. Thus, once the actuating means of any annunciator card has been actuated, silicon controlled rectifier 44 is inhibited from being actuated.

In order to aid in the trouble shooting of the annuciator circuit, test points T and T mentioned previously. are provided. By applying a signal at test point T which signal is comparable to the output signal level from generating means 14, alarm actuating means 18 should become actuated to provide an audible alarm and a flashing visual alarm. By maintaining the test signal at test point T and depressing acknowledgement switch 100, the audible alarm should turn off, and the visual alarm should provide a steady state visual indication. By removing the test signal from test point T the visual alarm indication should extinguish. Thus in this manner various functions of the annunciator circuit can be tested. Similarly, to aid in the breakdown testing of the overall circuitry, a steady state signal can be applied to test point T to drive transistor 92 on, and, if the visual alarm means is operating properly, a steady state visual alarm indication should be observable.

If it is desirable. a two position mode switch (not shown) can be inserted between terminals B and D. When one mode is selected and the switch is in the first position. terminal B is directly connected to terminal D and the annunciator circuit operates as previously described. When the other mode is selected and the switch is in the second position, terminal B is disconnected from terminal D. and the operation of the annunciator circuit is modified as follows. Terminal D is electrically coupled to terminal K of DC power means 30, so that transistor 46 is always biased on. Under these circumstances, once silicon controlled rectifier 44 is actuated, it can only be deactuated by opening acknowledgement switch 100.

Although the invention has been described with reference to a specific embodiment thereof, numerous modifications are possible without departing from the invention, and it is desirable to cover all modifications falling within the spirit and scope of this invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

I. An annunciator circuit comprising:

a. means for generating an output level signal in response to a sensed abnormal signal condition;

b. an audible alarm;

c. means for actuating said audible alarm upon initial recognition of the output level signal from said generating means and means responsive to the output level signal for deactuating said audible alarm if said audible alarm is still actuated when the abnor mal signal condition is corrected and the output level signal is extinguished; and

d. acknowledgement means electrically coupled to said alarm actuating means for deactuating said audible alarm only while the abnormal signal condition is sensed and for the duration of the output level signal.

2. An annunciator circuit according to claim l, further comprising:

a. visual alarm means;

b. a pulse generator; and

c. first logic driver means responsive to actuation of said alarm actuating means and output pulse signals from said pulse generator for intermittently driving said visual alarm means, whereby to cause said visual alarm means to flash and thereby pro duce an intermittent visual alarm indication.

3. An annunciator circuit according to claim 2, further comprising second logic driver means responsive to the output level signal from said generating means and to deactuation of said alarm actuating means for continuously driving said visual alarm means, whereby to cause said visual alarm means to produce a steady state alarm indication.

4. An annunciator circuit according to claim 1, wherein said generating means is comprised of a photoelectric transducer for converting the sensed abnormal signal condition in the form ofa DC or AC signal to the output level signal which is electrically isolated from the sensed abnormal signal condition.

5. An annunciator circuit according to claim 1, wherein said generating means is further comprised of a Hall Effect transducer for converting the sensed abnormal signal condition in the form of an AC or DC signal to the output level signal which is electrically isolated from the sensed abnormal signal condition.

6. An annunciator circuit according to claim 1, wherein said actuating means is comprised of:

a. a siiicon controlled rectifier having a gate terminal;

b. a differentiator circuit for responding to the initial recognition of the output level signal from said generating means to produce and apply a trigger signal to the gate terminal of said silicon controlled rectifier; and

c. a transistor electrically connected in series with said silicon controlled rectifier, said transistor having a base terminal responsive to the output level signal from said generating means for allowing current to pass through said silicon controlled rectifier and said transistor to said audible alarm after the trigger signal has been applied to the gate of said silicon controlled rectifier, for the duration of the output level signal, and prior to deactuation of said alarm actuating means by said acknowledgement means.

7. An annunciator circuit according to claim 6, wherein said acknowledgement means is comprised of a normally closed switch which is electrically coupled in series with said silicon controlled rectifier and a DC power source, whereby upon opening of said normally closed switch, the flow of current through said silicon controlled rectifier terminates.

8. An annunciator circuit according to claim 6, further comprising:

a. first out signal means generated upon actuation of said alarm actuating means for preventing actuation of other annunciator circuits while current is passing through said silicon controlled rectifier; and

b. means responsive to a generated first out signal means of another annunciator circuit for inhibiting the application of a trigger signal to the gate of said silicon controlled rectifier for preventing actuation of said alarm actuating means while an alarm actuating means of the other annunciator circuit is still actuated.

9. An annunciator card including therein an annunciator circuit, said annunciator circuit comprising:

a. means for generating an output level signal in response to a sensed abnormal signal condition;

b. means for providing a signal to actuate an audible alarm upon initial recognition of the output level signal from said generating means and means responsive to the output level signal for deactuating said audible alarm if said audible alarm is still actuated when the abnormal signal condition is corrected and the output level signal is extinguished; and

c. means within said card for regulating a DC power to said generating means and said alarm actuating means, said means for regulating the DC. power being electrically coupled to means of other annunicator cards for sharing power therebetween. 

1. An annunciator circuit comprising: a. means for generating an output level signal in response to a sensed abnormal signal condition; b. an audible alarm; c. means for actuating said audible alarm upon initial recognition of the output level signal from said generating means and means responsive to the output level signal for deactuating said audible alarm if said audible alarm is still actuated when the abnormal signal condition is corrected and the output level signal is extinguished; and d. acknowledgement means electrically coupled to said alarm actuating means for deactuating said audible alarm only while the abnormal signal condition is sensed and for the duration of the output level signal.
 2. An annunciator circuit according to claim 1, further comprising: a. visual alarm means; b. a pulse generator; and c. first logic driver means responsive to actuation of said alarm actuating means and output pulse signals from said pulse generator for intermittently driving said visual alarm means, whereby to cause said visual alarm means to flash and thereby produce an intermittent visual alarm indication.
 3. An annunciator circuit according to claim 2, further comprising second logic driver means responsive to the output level signal from said generating means and to deactuation of said alarm actuating means for continuously driving said visual alarm means, whereby to cause said visual alarm means to produce a steady state alarm indication.
 4. An annunciator circuit according to claim 1, wherein said generating means is comprised of a photo-electric transducer for converting the sensed abnormal signal condition in the form of a DC or AC signal to the output level signal which is electrically isolated from the sensed abnormal signal condition.
 5. An annunciator circuit according to claim 1, wherein said generating means is further comprised of a Hall Effect transducer for converting the sensed abnormal signal condition in the form of an AC or DC signal to the output level signal which is electrically isolated from the sensed abnormal signal condition.
 6. An annunciator circuit according to claim 1, wherein said actuating means is comprised of: a. a silicon controlled rectifier having a gate terminal; b. a differentiator circuIt for responding to the initial recognition of the output level signal from said generating means to produce and apply a trigger signal to the gate terminal of said silicon controlled rectifier; and c. a transistor electrically connected in series with said silicon controlled rectifier, said transistor having a base terminal responsive to the output level signal from said generating means for allowing current to pass through said silicon controlled rectifier and said transistor to said audible alarm after the trigger signal has been applied to the gate of said silicon controlled rectifier, for the duration of the output level signal, and prior to deactuation of said alarm actuating means by said acknowledgement means.
 7. An annunciator circuit according to claim 6, wherein said acknowledgement means is comprised of a normally closed switch which is electrically coupled in series with said silicon controlled rectifier and a DC power source, whereby upon opening of said normally closed switch, the flow of current through said silicon controlled rectifier terminates.
 8. An annunciator circuit according to claim 6, further comprising: a. first out signal means generated upon actuation of said alarm actuating means for preventing actuation of other annunciator circuits while current is passing through said silicon controlled rectifier; and b. means responsive to a generated first out signal means of another annunciator circuit for inhibiting the application of a trigger signal to the gate of said silicon controlled rectifier for preventing actuation of said alarm actuating means while an alarm actuating means of the other annunciator circuit is still actuated.
 9. An annunciator card including therein an annunciator circuit, said annunciator circuit comprising: a. means for generating an output level signal in response to a sensed abnormal signal condition; b. means for providing a signal to actuate an audible alarm upon initial recognition of the output level signal from said generating means and means responsive to the output level signal for deactuating said audible alarm if said audible alarm is still actuated when the abnormal signal condition is corrected and the output level signal is extinguished; and c. means within said card for regulating a DC power to said generating means and said alarm actuating means, said means for regulating the D.C. power being electrically coupled to means of other annunicator cards for sharing power therebetween. 